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I recently purchased a Whirlpool WOS51ES4ES electric oven from Home Depot with the intention of installing it myself. Our old oven is gas, so I need to run a new 240 circuit. The oven draws 20A.

I am currently at a loss regarding how to attach the pigtail connection that came with the oven to the 240 V wiring that I am going to run to the breaker box. I initially presumed that I need a junction box, and I'm not sure if the twist-on style are appropriate for these current levels. Additionally, I understand that there is an NEC requirement to be able to disconnect the oven from power locally (i.e. via unplugging it, or turning off a switch).

Is wiring up a 240 V junction box for this situation any different than a 120 V circuit?

Home Depot has been no help. Initially they told me to purchase four of these, connect like colors inside a junction box, and then just "wrap them up like hell with electrical tape". This sounded rather dangerous to me, so I came back during another shift to ask someone else. This time they said that my oven should have arrived with a plug (not a pigtail), and that I have to install a 240 V outlet to plug the oven into. I then also have to replace the pigtail with a corded plug by opening the oven, removing the pigtail from its attachment points (which they presumed were screw ring terminals) and install the corded plug by replacing like colors. Unfortunately, when I opened the oven, I found that the pigtail feeds into a wiring harness that runs to multiple places in the oven and there are no screw terminals in sight.

So I'm at a loss of what to do next. Surely there must be a way to install the oven without re-engineering it.

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  • @manassehkatz-ReinstateMonica It is a small 24 inch single oven, so yeah, it's on the small end. Whirlpool WOS51ES4ES – rothloup Dec 1 '19 at 21:22
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You need a 12/3+ground cable as a minimum to support this oven. However it would be a nice future-proofing trick to run 10/3+ground.

You can also run individual wires in conduit if you prefer, for the ultimate future-proofing. I would run 3/4" conduit, or 1" if able, as that will support any foreseeable future oven/range.

You must run neutral and ground separately.

Since this oven has a conduit whip, you will need to use a conduit connector and hardwire the oven to the junction box.

The breaker must be 20A.

There needs to be a junction box in the wall or mounted to the wall. I recommend a 4-11/16" steel square box because it has lots of room for future expansion, but a 4" square by 2-1/8" deep box will also suffice. This is high current stuff that will arc spectaularly, so it's no time to be fooling with plastic boxes. Metal boxes conduct heat well, spread heat instead of burning through, and will forestall a fire.

You can get a variety of front faceplates for either box to accommodate whatever you need - e.g. A NEMA 14-20 socket, or a blank cover plate with a knockout hole for mounting that wire whip.

Wire nuts are perfectly fine if they are properly done - use Ideal brand as they are electricians' favorites, this is the one time that "gorilla tight" is OK, and give the nuts a firm pull test (hold nut, yank each wire in turn). If you need tape to make it pass a pull test, that is bad technique, fix the technique.

I have never seen a disconnect switch for an oven.

  • Thanks for the information, but I don't think this addresses the question of how to attach the pigtail to the circuit. Are you also saying that a local disconnect is not required, since hardwiring would only allow the circuit to be de-energized at the breaker box? – rothloup Dec 1 '19 at 22:35
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    Edited @rothloup ... – Harper - Reinstate Monica Dec 1 '19 at 23:49
  • BTW: this particular oven needs to be hardwired (due to using a conduit whip) – ThreePhaseEel Dec 2 '19 at 0:59
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    ok, so what I'm hearing is that I should just wire this up in a metal junction box using wiring nuts. I'm probably overthinking this. – rothloup Dec 2 '19 at 1:25
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    422.30(B) Requires allows a circuit breaker to serve as the required disconnect if the breaker is within site or is lockable in accordance with 110.25 that requires the lock remain fixed in place with or without a lock. – NoSparksPlease Dec 2 '19 at 1:46
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20A vs. 30A

The general description says 20A. However, the specifications PDF says:

Models rated at 7.2 kW and below at 240 volts (5.4 kW and below at 208 volts) require a separate 30-amp circuit.

The specifications page specifically includes model WOS51ES4E.

My guess is that it is really designed for a 30A circuit, which is far more common for ovens than 20A.

Installation - 4-Wire

Follow the installation instructions. On page 5 there is a clear diagram for 4-Wire Cable from Home Power Supply. That is what you need to follow. As noted by Harper, this includes two hot wires and separate neutral and ground wires.

As far as how, the diagram includes:

D. 4-wire flexible cable from oven

Basically, the cable coming from the oven is in a pre-installed metal conduit. You connect that to a metal junction box. The other side of the junction box gets either a cable or wires in conduit depending on your local code and (if code allows your choice of cable or conduit) your preference. Generally cable is easier to run once but conduit is much easier if you ever need to change things.

Wire Size

Whether your wires are in conduit or cable, you need to size appropriately. The minimum for 20A is #12, for 30A #10 and for 40A #8. The manual says:

Use 8 gauge solid copper wire.

In reality, I think you are perfectly fine for this oven using #10 to go with the rated 30A breaker. I'm actually surprised they don't have a double listing (#10 for small ovens, #8 for large ovens) like they do for the breakers. But you can always upsize and putting in #8 now would take care of any reasonable future upgrade.

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